1. Field of the Invention
The present invention relates to a nonmagnetic substrate, a magnetic recording medium a magnetic recording drive, a method for manufacturing the magnetic recording medium and a method for transforming a surface of a layer into a rough surface.
2. Description of the Prior Art
In recent years, in the magnetic disk drive which is used as an external storage unit of the computer, a surface of a recording medium must be planarized to attain high density recording. In the magnetic disk drive employing a contact start-stop (CSS) scheme, there are however some cases wherein, since sticking is caused between a floating surface of the magnetic disk and a surface of the magnetic recording medium at the time when the magnetic disk drive is stopped, travel of the magnetic head is interfered with such sticking. For this reason, processing wherein the surface of the magnetic recording medium is processed to be rendered rough in such a degree that the sticking will not be caused, i.e., texture processing has been made as an endeavor to lower friction between the magnetic head and the magnetic recording medium In this case, it is very important to adjust height of projections in the texture processing since the spacing loss would be increased in proportion if the height of the projections are formed too higher.
For instance, as shown in FIG. 1, in the magnetic disk drive wherein the recording film 104 is formed on an aluminum substrate 101 on which an NiP film 102 is coated, an uneven shape is formed on the surface of the magnetic disk by forming mechanically textures on the surface of the NiP film 102. In FIG. 1, a reference 103 denotes a base film, and a reference 10 denotes a protection film.
In case the hard substrate such as the glass substrate on which mechanical textures are difficult to be formed must be employed, there has been disclosed the technique discussed in Patent Application Publication (KOKAI) 4-255908, for example. As shown in FIG. 2, in this technique, a film 112 of a low surface energy metal such as Ti is formed on a disk substrate 111, and a low melting point metal film 113 such as Al film is then formed thereon. If the low melting point metal film 113 is processed by heat treatment to condense Al particles, so that uniformly distributed projections are formed on the surface of the film 112 to thus form the rough surface. A reference 114 denotes a base layer; 115, recording layer; and 116, protection film. A technique has been disclosed in Patent Application Publication (KOKAI) 60-261017 wherein, by distributing microcrystals of Cr oxide on the surface of the substrate (magnetic tape), projections are formed on the surface of the recording layer which is formed on the substrate.
Alternatively, as shown in Patent Application Publication (KOKAI) 5-282666, there has been proposed a technique wherein, by mixing the fine particles into the protection layer formed on the surface of the recording layer, the surface of the recording substrate may be rendered rough while keeping the smooth surface of the recording layer.
In the conventional method for manufacturing the magnetic disk employing the mechanical texture processing shown in FIG. 1, however, it is hard to control a shape of the surface of the magnetic disk, and therefore sharp projections often exist. Such sharp projections are broken by the contact to the magnetic head, etc. to become dusts which sometimes cause the magnetic head crush. In the techniques disclosed in Patent Application Publication (KOKAI) 4-255908 or Patent Application Publication (KOKAI) 60-261017, the number of steps is increased in manufacturing process, and the manufacturing steps become thus complicated.
Furthermore, in the above three techniques, the base layer beneath the recording layer is formed to be rough, so that the surface of the recording layer per se would be rendered rough. Such coarse surface of the recording layer causes in general the medium noise. In contrast to this, the conventional technique recited in the above Patent Application Publication (KOKAI) 5-282666, the rough surface of the recording medium can be obtained by mixing fine particles into the protection layer formed on the surface of the recording layer etc., with the smooth surface of the recording layer being maintained. For this reason, the rough surface of the recording layer can be avoided, but there is caused a drawback that the device would be contaminated in the course of mixing fine particles such as SiO.sub.2 into the protection layer. In other words, although these fine particles are mixed into the protection layer by spraying the fine particles such as SiO.sub.2 in the film forming gas when the protection layer is sputtered, the sputtering apparatus is contaminated by the fine particles such as SiO.sub.2 to thus let a maintenance of the sputtering apparatus troublesome.